A seismological and petrological crustal model for the southwest of the Sierra de Pie de Palo, Province of San Juan

Resumen

A seismic velocity analysis from teleseismic receiver functions recorded in the southwestern flank of the Sierra de Pie de Palo (Western Sierras Pampeanas, Argentina), is compared with seismic properties directly calculated from lithological composition. The seismological results show an upper layer located in the first 13 km depth. A deeper contrast in seismic velocities is found at a depth of 28 km; the petrological results indicate a composition compatible with observed greenschist and amphibolite facies mafic rocks up to this depth. The receiver function measurements at 13 km and 28 km depths could be interpreted as two potential décollement levels that might have favoring a mechanism to thicken the whole crust, which produces a receiver function Moho signal located at 47 km depth. In addition, the lower crust between 28 km and 47 km exhibits high seismic P-wave velocities and Vp/Vs ratio (> 1.80) that are representative of a densification consistent with upper amphibolite to granulite/ecoglite
facies lithologies. Based on these results, the combined petrological and seismological analyses suggest the continuation of the same mafic-crust outcropping lithologies into the lower levels of the 47-km thickened crust, which could be part of the Pie de Palo Complex ophiolite belt or the Precordillera basement.